Abstract
The light reactions of oxygenic photosynthesis are mediated by multisubunit pigment-protein complexes situated within the specialized thylakoid membrane system. The biogenesis of these complexes is regulated by transacting factors that affect the expression of the respective subunit genes and/or the assembly of their products. Here we report on the analysis of the PratA gene from the cyanobacterium Synechocystis sp. PCC 6803 that encodes a periplasmic tetratricopeptide repeat protein of formerly unknown function. Targeted inactivation of PratA resulted in drastically reduced photosystem II (PSII) content. Protein pulse labeling experiments of PSII subunits indicated that the C-terminal processing of the precursor of the reaction center protein D1 is compromised in the pratA mutant. Moreover, a direct interaction of PratA and precursor D1 was demonstrated by applying yeast two-hybrid analyses. This suggests that PratA represents a factor facilitating D1 maturation via the endoprotease CtpA. The periplasmic localization of PratA supports a model that predicts the initial steps of PSII biogenesis to occur at the plasma membrane of cyanobacterial cells.
Highlights
The light-driven reactions of photosynthesis take place at a specialized membrane system, the thylakoids, that contains the essential protein complexes mediating photosynthetic electron transport, which include photosystem II (PSII),1 the cytb6f complex, PSI, and the ATPase
The periplasmic localization of PratA supports a model that predicts the initial steps of PSII biogenesis to occur at the plasma membrane of cyanobacterial cells
The idea of a specialized region where the biogenesis of photosynthetic membrane complexes takes place and that is spatially separated from the thylakoid membrane was further strongly supported by the recent observation that significant amounts of some PSII and PSI subunits are detectable in the plasma membrane of the cyanobacterium Synechocystis 6803 where they form chlorophyll-containing precomplexes [14]
Summary
The light-driven reactions of photosynthesis take place at a specialized membrane system, the thylakoids, that contains the essential protein complexes mediating photosynthetic electron transport, which include photosystem II (PSII),1 the cytb6f complex, PSI, and the ATPase. Protein pulse labeling experiments of PSII subunits indicated that the C-terminal processing of the precursor of the reaction center protein D1 is compromised in the pratA mutant.
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